he trains in front of the manager most days, he knows him and what he see's in training, that chance is earnt and not due just because you signed a contract and they paid 15m (which is nothing to them).
Maybe he had his chances over egged that he would break in, but its was clearly something he had to be a model professional and constantly show them he is ready even if the only chance is just during training.
They are any amounts of players who would kill to be in his position.
Maybe the manager is being a bit stubborn, but maybe he is not seeing the reaction he wants to see from him.
It's a tough break, but he still has to fight for his place like everyone else, I would tend to lean on the perception he can be cocky, a pain in the **** at times and he already had a bad reputation for his training, if he's not changed then its no surprise he isn't getting the chances ahead of the players who have all them appearances in the team already.
He needs/needed to dig right in and just concentrate on himself and make him self as ready as possible, frustrating but can't help think he gets sick and his immaturity shows when he is sick of things, and I bet Conte is looking for someone who instead of sulking just sucks it in and reacts by continuing to show the levels of training and discipline he expects from the team.